I seem to have an EFW file?

The file we send through is a normal ,ZIP file containing an Excel document, so not a .EXE.

An EFW extension is a Compressed .ZIP or executable .EXE file renamed by CA Security Centre to have a “.efw” extension; typically applies to e-mail attachments scanned by Computer Associates (CA) antivirus software. (In our case it would have been a .ZIP file). See this post at Filext for more information: http://filext.com/file-extension/EFWEFW zipped files may be opened by changing the file extension to “.zip” and opening the file with a decompression utility, such as WinZip or Stuffit Expander; executable files may be run directly by changing the file extension to “.exe” and opening the file.

Save the .efw file in a known location, and rename it with your chosen name (e.g. Rental Workbook v7) and add the extension …zip so the whole file name will become
“Rental Workbook v7.zip”. you should then be able to use the file as normal.